BUILDING CASE STUDY EDUCATING ENGINEERS
The boiler plant, calorifiers, chiller and CHP plant are housed in an adjacent energy centre
building’s atrium through transfer grilles set in the doors. A different natural ventilation solution is used for the classrooms on the second and third floors of the northern elevation. These rooms back on to a circulation corridor. Because the rooms are too deep to be ventilated by the façade alone, ducts have been installed above the corridor to form a link with the central lightwell to encourage air movement. The ducts are fitted with modulating dampers controlled by the BMS. For the postgraduate areas occupying the
top two floors on the building’s southern elevation, the natural ventilation solution has been combined with an air conditioning option to provide a mixed-mode solution. For the bulk of the year these are naturally ventilated using what Mooney describes as ‘a climate façade’. This is an 800 mm-deep, triple-skin glazed façade, with a double-glazed inner leaf and a single-glazed outer leaf covering the building’s southern elevation. The cavity between the inner and outer leaf is ventilated by louvres at the top of the façade. In winter, with the louvres closed, the
south-facing façade preheats the fresh air before it enters through windows opening
Ventilation Building management system system is controlled as
The natural ventilation strategy is helped by the exposed concrete soffits, which add thermal mass. In its basic format, the ventilation strategy is based on two rows of opening windows, one above the other. The high-level windows open and close under control of the building management system (BMS), while the lower windows can be opened manually. For the offices and laboratories on the eastern elevation the
30 CIBSE Journal January 2012
follows: l As the air temperature rises above summer and winter operational settings, the BMS will progressively open the
high-level windows. l In winter (from October to the end of April), if the lighting passive infrared sensor (PIR) detector indicates a room is occupied, and when CO2 levels exceed the zone set point, the BMS will open the high-level windows by 5%.
into the cavity. In summer, the louvres open to allow air to rise up and out of the cavity, preventing it from getting too warm before it enters the room. Switches in the window mullions allow the occupants to override the BMS and open and close the windows accordingly. The climate wall also features an automated external blind fitted on the outside to minimise solar gain. The natural ventilation system for the postgraduate areas operates until the internal temperature rises above 25C, at which point the displacement air conditioning system will kick in, with air supplied through the floor void. Openings in the dividing wall help to draw air across the postgraduate rooms and into the atrium. Mooney describes the atrium as ‘the building’s lungs’. Smoke ventilators mounted in the atrium roof open and close under control of the BMS to ventilate the area (the BMS also prevents the smoke extract fans running in this mode). Air is also drawn from the atrium into the building’s corridors where it provides tempered make-up air for the laboratories. The building includes several large lecture
l The windows will remain open unless the wind speed exceeds a pre-set level, it starts to rain or internal air
temperature falls. l The occupants can override the BMS using a wall-mounted rocker switch to open or close
the windows. l In addition, the occupants can also open the lower line of
windows manually. l At night the windows will open to remove excess heat under a night purge strategy.
theatres. These are kept comfortable using a displacement ventilation system, with fresh air supplied at 19C through swirl diffusers beneath each seat and extracted at high level. Mooney says the low-velocity swirl diffusers ‘create a microclimate around the occupants’. Additional mechanical cooling is provided by a packaged, air-cooled chiller. ‘During normal term times, mechanical cooling is not expected to be needed because the outside air temperature does not normally go above 19C from October to May,’ says Mooney. Cooling is also provided to groups of specialist laboratories tucked into the northwest corner of the building on the first, second and third floors. These rooms house experiments that need stable conditions throughout the year and are comfort cooled using active chilled beams. Some of the computer rooms are also provided with cooling and heating using chilled beams. Like the postgraduate areas, these too have a mixed-mode servicing strategy. ‘The building is complex due to the
number of mixed-mode strategies; if you were designing a commercial building with a focus on preliminary installation costs, you would only design for one HVAC system to guarantee a comfortable environment throughout the year,’ says Mooney. ‘The mixed-mode strategies will enable a reduction in the building’s environmental footprint.’
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